Heretofore, as a method for fluorinating all of C—H portions in a C—H containing compound to C—F, a method of employing cobalt trifluoride, a method of direct fluorination with fluorine gas, or a method of carrying out a fluorination reaction in an electrolytic cell using electrolyzed hydrogen fluoride as a fluorine source (hereinafter referred to as electrochemical fluorination) has been known. The method of employing cobalt trifluoride is one wherein the reaction is carried out at a high temperature by a gas-solid reaction, whereby isomerization or bond breakage takes place, and there is a problem that various types of by-products will form. In the case where a direct fluorination method is carried out with fluorine gas, a gas phase method or a liquid phase method has been known. However, the gas phase reaction has a problem that during the fluorination reaction, dissociation of C—C single bonds takes place, and various types of by-products will form. In recent years, a liquid phase method has been reported.
On the other hand, a method for fluorination in a liquid phase by reacting fluorine gas to a non-fluorine containing compound, has also been reported (U.S. Pat. No. 5,093,432). Further, a method for obtaining an acid fluoride compound by thermal decomposition of a perfluorinated ester compound having a carbon number of at least 16, has also been known, and it is disclosed that the compound can be obtained by direct fluorination of a hydrocarbon ester compound having a corresponding structure in a liquid phase with fluorine gas (J. Am. Chem. Soc., 120, 7117 (1998)).
The method of employing cobalt trifluoride or electrochemical fluorination has had a problem such that an isomerization reaction takes place or a problem such that breakage of the main chain, a re-union reaction, etc., may occur, and has had a drawback that the desired compound can not be obtained in good purity. In a case where a fluorination reaction is carried out in a liquid phase with fluorine gas, it is common to employ a solvent capable of dissolving fluorine gas, as the solvent for the reaction. However, a hydrocarbon compound as a starting material in a conventional method, usually has a low solubility in a solvent to be used for the fluorination reaction, and accordingly, the reaction is carried out in a very low concentration, whereby there has been a problem that the production efficiency is poor or a problem that the reaction will have to be carried out in a suspension which is disadvantageous to the reaction. Further, if it is attempted to fluorinate a hydrocarbon compound of a low molecular weight in a liquid phase, a problem has been observed such that the reaction yield tends to be remarkably low.
On the other hand, a fluorine-containing monomer such as a perfluoro(alkylvinyl ether) is useful as a starting material monomer for a fluorinated resin having heat resistance and chemical resistance. Heretofore, the perfluoro(alkylvinyl ether) has been industrially produced by a dimerization reaction of a perfluorinated epoxide or by reacting a perfluoroalkanoyl fluoride with a perfluorinated epoxide in the presence of an alkali metal fluoride to form a perfluoro(2-alkoxyalkanoyl)fluoride, followed by thermal decomposition. However, such a method has had a problem that control of the reaction of the dimerization reaction is difficult, and the price of the starting material is high and economically disadvantageous.